1. Field of the Invention
This invention generally relates to a process of forming a pattern for formation of a semiconductor device, more particularly to a process for forming a photoresist pattern used in forming a pattern of a layer in a semiconductor device.
2. Description of the Related Art
As a semiconductor device is highly integrated, high miniature and precision of critical dimension are essentially required. As a result, the conventional lithography system is met with limitations in enhancing performance.
A general process of forming a photoresist pattern used in forming a pattern of a layer in a semiconductor device, a photolithography process is described referring to enclosed drawing.
FIG. 1A-1B are cross-sectional views illustrating a process of forming a photoresist pattern according to a conventional method.
Referring to FIG. 1A, in order that a photoresist film 2 is to be coated well on a silicon substrate 1, a prime step is first performed to the surface of the silicon substrate 1. The prime step is a process to make a photoresist film attached strongly on the substrate 1, where the silicon substrate 1 is processed by a chemical etchant and is baked at a selected temperature during the prime step. Thereafter, the photoresist film is coated on the silicon substrate 1.
Referring to FIG. 1B, a predetermined portion of the coated photoresist film 2 is selectively exposed to light, and then the exposed portion is removed by a developing solution, thereby exposing the selected portion of the silicon substrate 1.
FIG. 2 and FIG. 3 show photoresist patterns formed according to the above-mentioned conventional method. FIG. 2 is a plane view showing a photoresist pattern for a space pattern such as a contact hole and FIG. 3 is a cross-sectional view taken along 3--3 line in FIG. 2. Symbol 5 is the outline of the space.
Referring to FIG. 2 and FIG. 3, at an edge portion of an exposed surface of the silicon substrate 1, there is a small amount of residue such as scum 3 and tail 4 from the developed photoresist film 2. The residue 3 and 4 is related with difference in the adhesion force between the silicon substrate 1 and the photoresist film 2.
In order to pattern a layer formed on a wafer, lithography process is performed on the layer. The lithography process is performed at an order of dehydration, photoresist spin coating, pre-bake, exposure, post exposure bake, developement, and inspection steps.
FIG. 4 shows a silicon substrate on which a layer for the patterning is formed when the dehydration step has been completed.
Referring to FIG. 4, the surface of the silicon substrate 1 is covered with a hydrophobic action radical "R".
Return to FIGS. 2 and 3, the hydrophobic action radical R increases the adhesion force between the surface of the silicon substrate 1 and the photoresist film 2 so that, after the developing step is performed to expose a selected portion of the silicon substrate 1 using a chemical solution, a small amount of residue of the photoresist film 2 exists around the outline 5 of the space.
In addition, the residue cause the generation of defects such as a tail and scum phonemena, which contributes to a decrease in product yield.
The defects negatively influences on measuring a pattern size in a semiconductor device, thereby decreasing the reliability of the semiconductor device.
The pattern size is measured at the contact interface 5 between the silicon substrate 1 and photoresist pattern 2 by an apparatus such as scanning electron microscope(SEM), and the measurement is performed by scanning an electron beam to the photoresist pattern 2 and the substrate 1. However, the defect of scum or exists on the exposed silicon substrate 1 and the contact interface 5, it becomes very difficult to measure the pattern size. In addition, though the measured value is attained, there is a degree of error.